Gaps in framing members after spray foamed ceiling
hi GBA’ers,
Our roof was recently spray foamed with 3.5″ of CCSF, and the rest of the rafters were stuffed with fiberglass batts. It is a hot roof with no venting. My concern is that a lot of the framing in the roof had blocking or boards sistered to each other, or have boards against each other where sections meet. They spray foamed the sheathing in the rafter bays, but what about the many small gaps between the boards that did not receive CCSF? Is this a major concern for condensation issues? Neither the insulator, builder, or the energy rater that looked over the install seemed concerned. But from my understanding, cold air can make it between the cracks in sistered framing and condense on the underside of the OSB. This is a vaulted ceiling, so if I need to foam/caulk every framing joint myself it would be quite an undertaking. Are these indeed not an issue? I haven’t seen anything like this mentioned/detailed in any spray foam articles. Another issue is that I found a small section of bare OSB which was covered with a batt. Can I reasonably fix this with canned spray foam? Those are all open cell correct?
thanks for any advice.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
It's best practice to put a bead of sealant between sistered joists/rafters at install time to air seal them. I doubt spray foam is going to be able to get into small gaps like that though, it needs bigger gaps to be able to get in and adhere. If you have a good interior side air barrier (such as drywall installed air tight), those small gaps probably aren't a problem, but you can seal them with caulk for extra insurance.
If you have any skylights in the vaulted ceiling, I WOULD seal any/all small gaps around the skylight wells though. Skylights complicate things like this, and make condensation more of an issue.
Bill
You should prevent warm, moist indoor air from reaching the cold sheathing. While wood is pretty resilient and can absorb and release moisture without problems for a long time, eventually if the moisture builds up enough, you'll get undesirable microbial action (aka mold and rot). If you're drywalling the space, that might be enough to keep moisture at bay, but it would be safer to seal the gaps. If the gaps are small, use a sealant; if they are large, use canned foam.
For the bay that didn't get foamed, you'll find trying to address it with canned foam slow, expensive and frustrating. (Guess how I know?...) I might tell the foam company to come back and finish the job, but more likely I would cut-and-cobble rigid foam into place and seal it with canned foam. That's not a reliable or easy way to insulate large areas, but for one bay it's not too bad.
thanks Michael, it's only a small part (roughly 3" round) of one bay and in a really awkward junction so probably impossible to cut and cobble. I was just wondering if there would be long term issues of using the open cell canned spray foam since the requirement for hot roofs on here is 2+ inches of CCSF. Getting the insulators to bring their truck and gear out just for that would probably delay the project for weeks even if I could get them to do it. Unfortunately, getting really air tight drywall is probably not going to happen due to timberframed rafters that are below the ceiling line, which was part of the reason I had to go with spray foam to begin with. Sealing every joint is going to be very tricky as they are ~23ft in the air in many places. Why isn't this standard practice for insulators if it truly is a serious mold issue?
The most important (and code-compliant) part of a hot roof is that the foam is air-impermeable, which canned foam will be if you're careful. Vapor-permeable foam can still allow moisture to move via diffusion but it won't happen as quickly as it would with an air-permeable insulation such as fiberglass or cellulose.
Standard practice on every project I've been on is for the insulators to seal any significant gaps in the framing. On jobs that I've managed, it's something that we discuss up front. But it's slow and finicky, so some installers may not do it as standard practice, and moisture issues rarely show up until 5-10 or more years have gone by, so contractors may not know that they are causing problems. Some projects will never have problems, even if the science says they should.
"moisture issues rarely show up until 5-10 or more years have gone by". Well that's a bit unsettling. Great stuff documentation doesn't mention closed cell that I can find, but I did see closed cell mentioned on one of their amazon listings for gaps and cracks so I guess I'll go with that. Getting the insulator to come back and fill in all framing gaps sounds like it's going to be an uphill battle as it does not seem to be "industry practice" around here, that and the builder has drywallers coming 2 days. I'll try to seal some of the gaps tomorrow, but it seems a bit hopeless as many of the gaps are up at the ridge, ~26ft in the air in some places and many gaps may now be hidden by batts. Seems pretty hopeless for me to get them all.
Picture for reference. These sorts of joints are all over the ceiling.
That's a pretty big gap -- you need to seal those. If it's more than about 1/4" or so, great stuff is probably the way to go here. I was thinking the usual tight gap with sistered framing members, which, while an air leak, isn't generally an "open void" like it appears that you have. If there are a lot of those -- as in every rafter -- I'd probably call the insulator back and say something along the lines of "you should have seen these gaps and filled them". If it's just a few, it's probably easier to just do it yourself.
For a small 3" hole in the foam, you can use Great Stuff (or equivalent), but you'll need to apply it in several layers, letting it cure between layers. If you try to fill a large hole in one shot, the inside won't cure right and will stay gooey (but won't be an issue the way a bad spray foam install can be).
The manufacturers of Great Stuff claim it's closed cell, but I don't think it's at the same level as the two part stuff the spray foam crews use. You should be OK using Great Stuff for smallish gaps and voids like you have, and many spray foam installers use similar stuff (the crew I typically subcontract spray foam work to likes OSI's Quadfoam product for filling voids in their spray foam installs). I like to use Loctite's TiteFoam in some places, especially where there is a need for a stronger and more solid foam for things like sealing in rigid foam panels.
If you have a lot of gaps to do, getting one of the foam guns to do the work instead of using the cans with straws will make things easier for you. If you go this route, be sure to get some of the snap-on plastic tips for the gun that let you "inject" the foam into the smaller gaps -- these are very helpful when filling skinny gaps like the one in the pic you posted. Stick the little tip as far into the gap as you can go so that you can apply foam to the back of the gap first, then let it expand until it oozes out the top a bit. With a little practice, you can get it so that it only oozes a little bit when it expands, which helps to ensure you fully fill the gap. When you're done, a fine tooth hacksaw blade held in your hand (or one of the holders that holds only one end of the blade) works great to trim the foam overfill flush with the bottoms of the rafters.
Bill
Thanks Bill, a lot of good info there. I'll probably have to tackle it myself. None of the trades here seem to care for these sorts of details. Getting up that high as a homeowner is just tough. I'll have to get a bigger ladder.
I should have also mentioned that if you use a foam gun, be sure to have a can of acetone on hand along with some paper towels. You have to clean the tip of the gun EVERY time you stop for more than maybe 10-15 seconds, and you have to clean it with acetone. What I typically do is hold a paper towel over the opening of the can of acetone, quickly invert the can to dampen part of the paper towel, that quickly wipe down the end of the spray foam gun, being especially careful to clean the area around the tip. If you aren't diligent about cleaning the gun, it will clog and basically become trash.
You might be able to borrow a ladder from one of your contractors if you ask nicely. Larger stepladders aren't cheap, and it sucks to buy one if you will only be using it a few times. If you do buy one, the type IA ladders (300 pound rating) are much more stable in the higher sizes, which is a big plus in terms of stability while you're working. I don't buy anything else. The extra weight of the ladder saves you a trip to the gym, but it's worth it for less chance of falling off while working.
Bill
Yeah they are pricey. Builder doesn't even have one big enough on hand. Builder claims that the gaps are small and that completely air sealing ceiling is impossible so not to worry. No clue how much moisture damage I would be looking at from the ~1/8" gaps. I might look into renting a ladder if that is a thing and just see what I can do by this weekend as the drywallers are coming early next week. I don't think I'll even be able to see all the gaps without removing the fiberglass batts from the bays.
I've searched online and I haven't seen a single example that looks like the joints of framing have been intentionally caulked/foamed. I suppose it could be a combination of the pictures being mid-install and not on unvented hot roofs, but is it just standard practice to leave gaps between framing unsealed? Here is an article from FHB, notice the large gap between framing members to the right: https://www.greenbuildingadvisor.com/article/getting-spray-foam-right
here is another article, can't tell from the picture but presumably the rafter to beam connections would all have some degree of gaps but no foam is put at the end of the joint to seal them: https://www.finehomebuilding.com/project-guides/insulation/spray-foam-insulation. This installation has what looks like a fairly complicated set of framing connections that are left exposed: https://www.greenbuildingadvisor.com/article/does-this-roof-need-more-foam. Perhaps there just isn't enough surface area of the OSB exposed by these small gaps to really matter?
This is the one problem with spray foam roofs. You have a lot of 3d shapes you are trying to seal, impossible to do a perfect job for example:
https://www.greenbuildingadvisor.com/question/ice-dams-on-almost-complete-new-construction-house
https://www.greenbuildingadvisor.com/question/air-seal-conjoined-trusses
The question is how critical is to to get these air tight and does the bit of snow melt matter. These spray foam hot roofs have been built for a while but not long enough to know for sure. My gut feel, beside the bit of icing up, small air leaks don't matter but if you get a large one, it can move a fair bit of moisture into your roof sheathing and cause rot down the road.
My $0.02 is do your best to seal things up but don't go crazy.
Air leaks through spray foam are very hard to visually find, may times it is not in obvious spots. A blower door (or a DIY box fan mounted in a window) and some smoke sticks can help you track down the larger ones. This would have been much easier in the winter time when you can use an IR camera to see leaks, If the house is conditioned, you might still be able to see something on a hot day though.
Yeah I had that question when blower door and Ir cameras were mentioned in the article. Even if I had hvac commissioned (not until after drywall and painting), I’m doublful these small cracks between framing would show up on IR or smoke tests as the gaps are small and the osb is sealed above with peal and stick ice and water shield. I doubt any air is actually leaving the house, just potentially condensing in small gaps. I’m not sure there really is a way to test for that.
Hmmh, the consensus from those posts seemed to be it may have been more from thermal bridging than air leaks and his smoke tests and ir cameras didn’t show leaks and were not helpful (but ach50 of only 1.8). The consensus from those posts is that issues like ice dams are inevitable on hot roofs. I’ll just do what I can.
On inspection I found 4 areas with bare roof sheathing exposed. I got 3 of the smaller ones with several cans of the pro gaps and cracks using the gun and plastic tip extension recommended above. The fourth one however is quite large, about 5sqft and out of reach for me. Insulator claims that shoving batts in there will protect it, but this seems to be a code violation from what I can see. The city inspector already came by, passed the insulation, and said they did a fantastic job. Am I just overly OCD from reading too much GBA?
No, batts will NOT "protect it" -- you need an impermeable insulating material (like spray foam), and it should be fully adhered to the underside of the sheathing to ensure protection (which is what spray foam does).
I would try to get your insulator to come back and spray foam that missed area, since they should have caught that the first time. If that's too much hassle, try one of the very small 12 board foot two-part spray foam kits (Dow makes one, possibly other manufacturers do too). These kits are ridiculously expensive for what they are (last I checked, they were around $80), but they're really the best option for these very small areas. You'll probably need 2-3 kits though, so check that the next step up (200 board foot) kit isn't going to be cheaper -- then get whichever option is cheapest. The 12 board foot kits are probably about 5-8 square feet 1" thick in reality, since they never seem to go as far as advertised. You'll want to keep the cans submerged upside down in a bucket of hot (but not so hot you can't keep your hand in it) water while you're spraying too to make sure you get the most out of the kit.
Bill
No, batts will NOT "protect it" -- you need an impermeable insulating material (like spray foam), and it should be fully adhered to the underside of the sheathing to ensure protection (which is what spray foam does).
I would try to get your insulator to come back and spray foam that missed area, since they should have caught that the first time. If that's too much hassle, try one of the very small 12 board foot two-part spray foam kits (Dow makes one, possibly other manufacturers do too). These kits are ridiculously expensive for what they are (last I checked, they were around $80), but they're really the best option for these very small areas. You'll probably need 2-3 kits though, so check that the next step up (200 board foot) kit isn't going to be cheaper -- then get whichever option is cheapest. The 12 board foot kits are probably about 5-8 square feet 1" thick in reality, since they never seem to go as far as advertised. You'll want to keep the cans submerged upside down in a bucket of hot (but not so hot you can't keep your hand in it) water while you're spraying too to make sure you get the most out of the kit. If you use the larger 200 board foot kit, just warm up the tanks before you use them. You want the tanks up around 80*-85*F or so, but don't let them get too hot. An easy way to warm them up is to leave them in a bathroom for half a day with a space heater running.
Bill
Thanks Bill. What is the throw on these units? Would they be able to hit and stick to something 3-4 ft out of my reach? I’m wondering if I shoukd try to jerry rig a long 1/2” pvc pipe to my pro gun and see if I can just dump several single component cans at it from a distance.
I don't think there is any way you're going to be able to spray over such long distance. The max you can have the gun away from the surface is maybe 8-12" or so tops. I don't think I've every held it quite that far myself (I've never really measured though :-)
You could probably use your great stuff gun the way you describe, but you need something that will fit tight to the tip of the gun. Maybe 3/8" PEX? 1/4" or 5/16" tubing? Find something that will make a tight fit over the end of the gun just like the snap-on plastic tips do. You can then run that smaller tubing through some 1/2" PVC pipe to make it rigid enough that you can aim it from a distance. If you just try to blow foam into the end of the pipe, it's just going to block the pipe and come back out at you towards the gun, making a mess. With the tight-fitting tube, the foam will be forced to the far end of the tube before it can start expanding, which is what you want.
If you try doing this with one-part foam (which I don't recommend when you have this large of an area to cover), you need to do multiple layers about 1" thick. If you try to fill the entire area to full depth all at once, the foam in the middle will not cure correctly and will stay gooey, or just leave a big bubble-like void. You need a full depth fill of proper foam.
Note that there are larger cans of one-part foam available (Kraken Bond, etc.) that may be useful here.
Bill
sounds like "fun", I'll give it a shot. I tried a tip I saw in FHB once by using some romex tubing duct taped to the end of the gun to get in hard to reach areas. The foam kept eventually finding a way out of the tape as an easier path than the 2ft romex tube. I might try some of that emergency pipe sealing tape and see if that might hold out enough pressure to get the foam through the long tube.
If you go to the hardware store, you can find some flexible vinyl tubing (the clear stuff) that will fit tightly over the end of the gun with no tape needed to make a good seal. I think it's 5/16", maybe 3/8", but there is a standard size that is a pretty good fit.
Bill
Operation successful. It took 6 cans of great stuff pro gaps and cracks and about 6 hours of very slow filling. The sheathing goes back a lot further than the picture suggests and ends in a triangular point about 5 feet in. Method was to fill the point, then slowly creep pipe back a bit at a time. Tough as I couldn’t actually see the end. There are likely voids or parts of foam that won’t cure correctly, but this was a best effort approach. The apparatus, which I Christened “Bill”, consisted of a pro gun with 3/8” vinyl tubing from orange places plumbing dept. that in turn was put into 1/2 pex, but with the added weight of the foam it started sagging, so that pex was then put into 1” pvc. I initially tried emptied out romex and then 1/4 vinyl forced up the gun barrel and taped with guerrilla plumbing seal tape. No tape ever worked, as the pressure from the gun eventually will force its way through any tape it seems. The 1/4 did not hold up. Partly due to I initially used gun cleaner through it and that seems to have weakened the pipe. 3/8 vinyl just over the tip with no tape was the only method that worked for me. I wouldn’t count on being able to reuse this.
Your efforts are likely to improve things, and remember that this is a one shot deal, so once you’re done, you’re done.
The gun cleaner is acetone in pressurized can, so it’s a pretty potent solvent and it can mess up many plastic materials.
Bill